As more and more electric appliances are brought to the market, the various electric appliances have played an increasingly important role in our daily lives. However, fire accidents caused by such appliances have also become an issue. According to the National Fire Agency of Taiwan's Ministry of the Interior, the total number of reported fire accidents in Taiwan in 2010 is 2186, of which more than one third, or 744 cases, can be attributed to electric appliances. Therefore, in order to create a safer living environment, it is imperative for the general public to have proper concepts and habits regarding the use of electricity and to choose electric appliances that are safe in design. Generally speaking, an electric appliance is almost always provided with a power switch for controlling the electric current flowing into and out of the appliance, so that users can switch on and off the appliance conveniently.
Referring to FIG. 1, a conventional power switch 1 includes a housing 11, a key 12, a first conductive plate 131, a second conductive plate 132, a thermally actuated metal plate 14, a C-shaped spring 15, a third conductive plate 133, a light-emitting unit 16, and a pressing element 17. The housing 11 forms a receiving space 111 therein and has an opening 112 on the top surface, wherein the opening 112 communicates with the receiving space 111. The middle portion of the key 12 is pivotally connected to the inner periphery of the opening 112. The bottom of the key 12 is provided with a first pushing portion 121 and a second pushing portion 121, which two pushing portions are proximate to two opposite ends of the key 12 respectively and are received in the receiving space 111.
As shown in FIG. 1, the first conductive plate 131 is fixedly provided adjacent to an inner lateral side of the housing 11. The top end of the first conductive plate 131 is received in the receiving space 111 and provided with a first contact P3. The bottom end of the first conductive plate 131 extends out of the bottom surface of the housing 11. The second conductive plate 132 is fixedly provided on the housing 11 and has a bottom end extending out of the bottom surface of the housing 11 and a top end received in the receiving space 111. The thermally actuated metal plate 14 has one end fixed to the top end of the second conductive plate 132 and a free end extending toward the lateral side of the housing 11 where the first conductive plate 131 is located. Referring to FIG. 2, the thermally actuated metal plate 14 is formed with a generally U-shaped groove 141 which defines a resilient tongue 142 of the thermally actuated metal plate 14. The free end of the resilient tongue 142 extends toward the second conductive plate 132 and can move above or below the groove 141 when the free end of the thermally actuated metal plate 14 is subjected to or not subjected to an applied force. A second contact P4 is provided on the resilient tongue 142, proximate to the free end thereof, and corresponds in position to the first contact P3 (see FIG. 1). The C-shaped spring 15 has one end engaged with the free end of the resilient tongue 142 and an opposite end engaged with the end of the thermally actuated metal plate 14 that is connected to the second conductive plate 132. As shown in FIG. 1, the C-shaped spring 15 corresponds in position to the first pushing portion 121 so that when the first pushing portion 121 is moved downward, the C-shaped spring 15 is pushed by the first pushing portion 121 and hence drives the free end of the resilient tongue 142 downward, thereby bringing the second contact P4 into electrical connection with the first contact P3. When the second pushing portion 122 is moved downward, the free end of the thermally actuated metal plate 14 is pushed downward by the second pushing portion 122 and generates a resilient restoring force that drives the free end of the resilient tongue 142 upward; as a result, the second contact P4 is separated from the first contact P3.
Referring to FIGS. 1 and 2, the third conductive plate 133 is fixedly provided proximate to an opposite inner lateral side of the housing 11. The top end of the third conductive plate 133 is located in the receiving space 111 while the bottom end of the third conductive plate 133 extends out of the bottom surface of the housing 11. The light-emitting unit 16 is housed in the key 12 and has two electrodes 161 respectively and electrically connected to the second conductive plate 132 and the third conductive plate 133. The pressing element 17 has one end pressing against the electrode 161 that is connected to the second conductive plate 132 and an opposite end pressing against the third conductive plate 133. The pressing element 17 includes a spring 171 and an insulating rod 172. Due to the spring 171, the electrode 161 that is connected to the second conductive plate 132 is pressed tightly against the second conductive plate 132. The insulating rod 172, on the other hand, prevents the pressing element 17 from connecting the second conductive plate 132 and the third conductive plate 133 electrically.
The temperature of the thermally actuated metal plate 14 rises when the power switch 1 is turned on, and the rise in the temperature varies with the current flowing through the thermally actuated metal plate 14 per unit time. Once the temperature of the thermally actuated metal plate 14 reaches a memory temperature, the thermally actuated metal plate 14 begins to deform. Therefore, referring to FIG. 2, should the current through the power switch 1 exceed a rated current, the thermally actuated metal plate 14 will deform in such a way that the resilient tongue 142 springs upward and causes separation of the first contact P3 and the second contact P4. In other words, the power switch 1 will be automatically turned off upon a current overload, with a view to protecting the circuit of the electric appliance connected to the safety switch 1.
While power switches similar to the power switch 1 are now in extensive use, the power switch 1 still has certain drawbacks in terms of production, as explained below with reference to FIGS. 1 and 2:
(1) As the light-emitting unit 16 is configured to have one electrode 161 clamped between the third conductive plate 133 and the inner wall of the housing 11 and the other electrode 161 clamped between the second conductive plate 132 and the spring 171, the assembly process must be conducted slowly and carefully to ensure proper electrical connection between the light-emitting unit 16, the second conductive plate 132, and the third conductive plate 133. Besides, an assembly worker often has to move several components in order to install one, thus lowering production efficiency.
(2) The foregoing assembly process cannot be done other than manually, so the quality of assembly depends mainly on the assembly workers' experience. To achieve a high yield rate, a manufacturer must take considerable time training the assembly workers, which nevertheless results in high labor costs.
(3) Given the current design trend of the power switch 1 toward increased compactness, the interior space of the housing 11 is very limited. Because of that, the electrodes 161 of the light-emitting unit 16 are often bent to save space. However, if the electrodes 161 are bent so much that they contact with the C-shaped spring 15, short circuits will occur. To prevent such short circuits, the electrodes 161 must be parted during assembly to avoid contact with the C-shaped spring 15, and this explains why the adjustment of the electrodes 161 always takes a lot of time and effort. The manual adjustment also hinders automated installation of the light-emitting unit 16 and compromises the yield rate of the power switch 1. Moreover, the light-emitting unit 16 tends to shake slightly when the key 12 is moved back and forth. As time goes on, the accumulated effect of such slight shakes may bring the electrodes 161 closer to, or even into contact with, the C-shaped spring 15, thereby causing dangerous short circuits.
(4) The second conductive plate 132 must be bent several times so as for its top end to serve as a supporting surface for the thermally actuated metal plate 14, and for its bottom end to extend out of the housing 11 and be adequately spaced from the first and the third conductive plates 131, 133. This bent structure of the second conductive plate 132, however, requires the use of more material than a straight structure and incurs higher material costs. Additionally, as the lower bent portion of the second conductive plate 132 is adjacent to the top end of the first conductive plate 131, the first conductive plate 131, if tilted when installed, is very likely to contact with the second conductive plates 132, thus rendering the power switch 1 useless. Furthermore, if the power switch 1 is used in a circuit configured for a large current, an electric arc may take place between the first and the second conductive plates 131, 132 should the lower bent portion of the second conductive plate 132 be too close to the first conductive plate 131. Such electric arcs are severe safety hazards because they not only can damage the power switch 1 but also may cause fire accidents.
Please refer to FIG. 3 for the structure of another conventional power switch 2, which includes a key 22 having a pivot hole 221 at one end. The pivot hole 221 is pivotally connected with one end of a push/pull bar 25. The other end of the push/pull bar 25 passes through a through hole (not shown) of a thermally actuated metal plate 24 and is engaged with the free end of the thermally actuated metal plate 24. When the key 22 is pressed, the push/pull bar 25 is driven by the key 22 to push or pull the thermally actuated metal plate 24, causing the free end of the thermally actuated metal plate 24 to swing up or down, and a resilient tongue 241 of the thermally actuated metal plate 24 to swing correspondingly. As a result, a second contact P6 which is provided at the free end of the resilient tongue 241 is separated from or brought into contact with a first contact P5 at the top end of a first conductive plate 231. This conventional power switch 2 has the same drawbacks as the power switch 1, as explained in further detail below:
(1) Referring to FIG. 3, the power switch 2 has a light-emitting unit 26 whose two electrodes 261 are respectively clamped between a second conductive plate 232 and the inner wall of a housing 21 and between a third conductive plate 233 and the inner wall of the housing 21. Therefore, during the manufacturing process, an assembly worker must place the light-emitting unit 26 in the housing 21 and then insert the electrodes 261 in place while bending the electrodes 261 carefully. After that, the second conductive plate 232 and the third conductive plate 233 are assembled to the housing 21. In particular, the assembly worker must grip the free end of each electrode 261 and route the electrodes 261 below the second and the third conductive plates 232, 233 respectively, so as to ensure that the electrodes 261 are held in place by the two conductive plates 232, 233 respectively. If the second conductive plate 232 or the third conductive plate 233, once assembled to the housing 21, fails to hold the corresponding electrode 261 in position, the assembly worker must detach the conductive plate in question from the housing 21 and install it again. The detachment and reinstallation process not only lowers production efficiency but also may damage the components involved, thus incurring additional costs.
(2) As the key 22 relies on the push/pull bar 25 to drive the thermally actuated metal plate 24 and thereby connect or separate the first and the second contacts P5, P6, the distance between the two ends of the push/pull bar 25 is crucial to the operation of the switch 2. If the distance is too great, the push/pull bar 25 will have problem pulling the thermally actuated metal plate 24; as a result, the second contact P6 will never contact with the first contact P5. If the distance between the two ends of the push/pull bar 25 is too small, the push/pull bar 25 cannot push the thermally actuated metal plate 24 properly, and because of that, the second contact P6 will not separate from the first contact P5. Since the push/pull bar 25 is a slender and hence rather fragile metal rod, it cannot be installed by an automated process. The assembly worker must take extra care in order not to bend the push/pull bar 25; otherwise, the distance between the two ends of the push/pull bar 25 may be altered, which is detrimental to the function of the switch 2.
(3) The assembly process described above must be carried out by hand and therefore relies heavily on the assembly workers' experience. In order to increase yield rate, a manufacturer must spend a lot of time training the assembly workers, and yet high labor costs ensue.
(4) The second conductive plate 232 must be bent several times so that its top end provides a supporting surface for the thermally actuated metal plate 24 and its bottom end extends out of the housing 21 and is properly spaced from the first and the third conductive plates 231, 233. This bent structure, however, increases the material required for making the second conductive plate 232 and thus incurs a high production cost.
The foregoing switches are only two examples of the conventional power switches. The various conventional power switches on the market, though different in design, have more or less the same drawbacks that make automated production impossible; consequently, the burden of high labor costs cannot be relieved from the manufacturers' shoulders. The soaring prices of metals also contribute to high material costs. More importantly, the conventional power switches have safety concerns that have yet to be properly addressed. Hence, it is a pressing issue for power switch designers and manufacturers to simplify the overall design and components of a power switch so that a light-emitting unit can be easily installed in the power switch by an automated process, thus not only reducing the labor and material costs of the power switch, but also preventing short circuits which may otherwise occur if the two electrodes of the light-emitting unit contact with a C-shaped spring.